Study On The Main Chemical Compositions Of Bamboo And Their Modification By Click Chemistry And Grafting Via ROP

Currently, the main focus from people has been on the energy crisis and environmentalpollution. The conversion of lignocellulosic biomass into biofuels, chemicals, andbiomaterials is an alternative way for the supplement and/or replacement of petroleum-basedproducts. As one of the most important biomass, bamboo is rich-resource in China. In thisstudy, a series of research was carried out to focus on the isolation and purification of themain chemical compositions （starch, cellulose, hemicelluloses, and lignin） of bamboo andidentification of their structure as well as the biodegradation and chemical modification,which will provide the theory and technology for the high-valued utilization of bamboo. Theresearch and the results are described as follows:（1） Alkalisoluble hemicelluloses were fractionated by graded precipitation at ethanolconcentrations of0,15,30,45,60, and75%（v/v）. Chemical composition and structuralfeatures of the six hemicellulosic subfractions were investigated by a combination of sugaranalysis, GPC, FT-IR, GC-MS,1D (¹H and¹³C) and2D （HSQC） NMR spectra, and thermalanalysis. The results showed that the bamboo （Phyllostachys bambusoides f. shouzhu Yi）hemicelluloses were O-acetylated4-O-methyl-glucuronoarabinoxylans consisting of a linear（1â†'4）-β-D-xylopyranosyl backbone decorated with branches at O-3of α-L-arabinofuranosyl（5-12mol%） or at O-2of4-O-methylglucuronic acid units and acetyl groups （0.8-11mol%）.The molecular weights of these polysaccharides ranged between13400and67500g/mol. Itwas also found that more branched hemicelluloses were precipitated at higher ethanolconcentrations. Moreover, xylo-oligosaccharides （XOS） with DP1-6were produced byenzymatic hydrolysis of hemicelluloses and the total yields of XOS were range of21.5to40.6%. At the same time, the effect of structural features of hemicelluloses on the preparationof XOS by enzymatic hydrolysis was also discussed. In addition, Starch from bamboo wasevaluated by means of solid-state¹³C CP/MAS NMR and X-ray diffraction.（2） Seven lignin fractions from bamboo Phyllostachys incarnata Wen were isolated bythe sequential extractions with distilled water,0.5%and1%NaOH,60%ethanol containing1%NaOH, and3%,5%and8%NaOH. The chemical composition and structuralcharacterization of the milled wood lignin （MWL） and alkali-fractionated lignins werecomparatively investigated using FT-IR, GPC,2D HSQC, alkaline nitrobenzene oxidation,and thermal analysis. It was found that bamboo MWL （S/G¹.3） is of SGH type with aconsiderable amount of esterified p-coumaric acid and etherified ferulic acid. Molecularweights of3,320g/mol for MWL and varying weights between970and3,430g/mol for the alkali-fractionated lignins were obtained. Moreover,2D HSQC of MWL showed apredominance of β-O-4’ linkages （65%）, followed by β–β’ linkages （15%） and lower amountsof β-5’（7%）, β-1’（4%）,5–5’（4%） linkages, and cinnamyl acetate end groups （5%）. Inaddition, a percentage （⁴5%） of the lignin side chain was found to be acylated at theγ-carbon. However, the alkali-fractionated lignins lost parts of these linkages duringsuccessive alkaline fractionation processes.（3） Propargyl cellulose was synthesized by etherification of bamboo Phyllostachysbambusoide cellulose with propargyl chloride in DMA/LiCl in the presence of NaH. On theother hand, the functional azide groups were introduced onto the chitosan chains byDCC-catalyzed reacting chitosan with4-azidobenzoic acid in [Amim]Cl/DMF. The synthesisconditions of reactions were respectively optimized. Meanwhile, the regioselectivity ofpropargylation on anhydrous glucose unit was determined. Subsequently, the novelcellulose-click-chitosan polymer was obtained via click reaction between the terminal alkynegroups of cellulose and the azide groups on the chitosan backbone. The successful binding ofcellulose and chitosan was confirmed and characterized by FTIR and CP/MAS¹³C NMRspectroscopy. TGA analyses indicated that the cellulose-click-chitosan polymer had a higherthermal stability than that of cellulose and chitosan as well as cellulose-chitosan complex.More interestingly, some hollow tubes with near millimeter length were also observed bySEM.（4） Xylan-g-PPO was firstly synthesized by grafting xylan from bamboo （Phyllostachysbambusoides） with poly（propylene oxide）（PPO） chains using the Al（Oi-Pr）3-initiatedring-opening polymerization. The effects of reaction conditions on the GD, molecular weightsand molecular weight distributions of xylan-g-PPO were also discussed. Furthermore, thecarboxymethyl groups were introduced onto xylan-g-PPO by microwave irradiation forsynthesis of carboxymethyl xylan-g-poly（propylene oxide）. The resulted xylan-g-PPO andCMX-g-PPO were well characterized by FTIR and¹³C NMR.